Note: Descriptions are shown in the official language in which they were submitted.
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PNEUMATIC TIRE
TECHNICAL FIELD
[0001]
The present invention relates to a pneumatic tire provided with a tread
pattern.
BACKGROUND
[0002]
A conventional tire is known that is used all year long as an all-season
tire and that has four circumferential main grooves, a region of inside land
portion partitioned by two inner circumferential main grooves on the inside,
and
regions of two intermediate land portions partitioned by outer circumferential
main grooves and the inner circumferential main grooves (see Patent Document
1). In the tire in Patent Document 1, lug grooves are provided in the region
of
the inside land portion and in the regions of the intermediate land portions,
and
the lug grooves in the regions of the two intermediate land portions extend in
an
inclined manner in the same orientation with respect to the tire
circumferential
direction, and the lug grooves in the region of the inside land portion extend
in
an inclined manner in a different orientation with respect to the tire
circumferential direction than the lug grooves in the regions of the
intermediate
land portions. Snow performance is maintained while dry performance can be
improved in the tire according to Patent Document 1.
PRIOR ART DOCUMENT
Patent Document
[0003]
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Patent Document 1: Japanese Unexamined Patent Application
Publication No. 2010-168006A
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0004]
An all-season tire is desirably provided with a tire performance that can
handle various road surface conditions such as dry, wet, or snow-covered road
surfaces. However, the tire in Patent Document 1 does not exhibit a sufficient
balance in abrasion resistance on dry road surfaces, wet performance, and snow
performance. Specifically, abrasion resistance on dry road surfaces decreases
when wet turning performance and steering stability on snow are improved.
The present invention provides a pneumatic tire having an excellent
balance in abrasion resistance on dry road surfaces, wet turning performance,
and steering stability on snow.
Means to Solve the Problem
[0005]
One aspect of the present invention is a pneumatic tire. The pneumatic
tire includes:
a bead;
a side wall;
a belt layer;
a carcass layer; and
a tread portion having a tread pattern; wherein
the tread pattern includes:
a circumferential main groove group having four circumferential main
grooves extending parallel to the tire circumferential direction, the four
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circumferential main grooves including two outer circumferential main grooves
and two inner circumferential main grooves interposed by the outer
circumferential main grooves with a tire center line passing between the inner
circumferential main grooves;
a plurality of lug grooves transecting a region of an inside land portion
partitioned by the two inner circumferential main grooves and through which
the tire center line passes, and regions of two intermediate land portions
each
partitioned by one of the outer circumferential main grooves and one of the
inner circumferential main grooves, to form a plurality of land portion blocks
in
the inside land portion and in the intermediate land portions; and
circumferential shallow grooves that are provided in the respective
regions of the intermediate land portions, that extend in the tire
circumferential
direction, and that have a groove depth that is less than a groove depth of
the
circumferential main grooves; wherein
an orientation of a groove inclination with respect to a first direction of
the tire circumferential direction of lug grooves provided in a region of one
intermediate land portion of the two intermediate land portions is identical
to
an orientation of a groove inclination with respect to a second direction that
is
opposite to the first direction of the tire circumferential direction of
second lug
grooves provided in a region of another intermediate land portion of the two
intermediate land portions when the lug grooves provided in each of the two
intermediate land portions advances from the outer side in the tire width
direction to the inner side in the tire width direction, and the lug grooves
provided in the respective regions of the intermediate land portions have a
curved portion that is curved so that the groove inclination approaches the
tire
circumferential direction at a position of intersection with the
circumferential
shallow groove; and
lug grooves that are provided in the inside land portion extend in an
orientation of a groove inclination that is different with respect to the tire
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circumferential direction from lug grooves provided in the respective regions
of
the intermediate land portions, when the lug grooves advance from the outer
side in the tire width direction to the inner side in the tire width
direction.
[0006]
The respective regions of the intermediate land portions preferably have
sipes that extend so as to be parallel to the lug grooves provided in the
respective regions of the intermediate land portions, and the sipes are
blocked
within the intermediate land portions without connecting with the inner
circumferential main grooves.
[0007]
The sipes preferably extend in a zigzag manner while deflecting in a
direction orthogonal to an extension direction of the sipes in the tire width
direction and extend in a zigzag manner while deflecting in a direction
orthogonal to a sipe depth direction of the sipes from a tread surface toward
a
bottom portion of the sipes in a region on the inner side of the
circumferential
shallow grooves.
[0008]
The sipes preferably extend in a linear manner in a region on the outer
side of the circumferential shallow grooves in the tire width direction, and
extend in a planar manner in a depth direction of the sipes from a tread
surface
toward a bottom portion of the sipes.
[0009]
Moreover, shoulder land portions are provided in regions on the outer
side of the circumferential main groove group in the tire width direction, and
regions of the shoulder land portions have shoulder lug grooves,
provided therein, extending from the outer side in the tire width direction
toward the outer circumferential main grooves, and the shoulder lug grooves
are
blocked part way through without connecting with the outer circumferential
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main grooves, whereby the shoulder land portions preferably form continuous
land portions that extend continuously in the tire circumferential direction.
[0010]
Moreover, shoulder land portions are provided in regions on the outer
side of the circumferential main groove group in the tire width direction, and
regions of the shoulder land portions have shoulder lug grooves provided
therein, extending from the outer side in the tire width direction toward the
outer circumferential main grooves, and
a maximum groove width of the shoulder lug grooves is preferably
greater than a maximum groove width of the lug grooves provided in the region
of the inside land portion and in the regions of the intermediate land
portions.
[0011]
The shoulder land portions are provided with shoulder sipes provided
therein, extending from the outer side in the tire width direction toward the
outer circumferential main grooves, and
the shoulder sipes include a first portion extending in a linear manner in
an extension direction of the shoulder sipes and extending in a planar manner
in
a sipe depth direction of the shoulder sipes from a tread surface toward a
bottom portion of the shoulder sipes, and a second portion extending in a
zigzag
manner while deflecting in a direction orthogonal to the extension direction
of
the shoulder sipes and extending in a zigzag manner while deflecting in a
direction orthogonal to a sipe depth direction of the shoulder sipes from a
tread
surface toward the bottom portion, and the shoulder sipes change from the
first
portion to the second portion while advancing from the outer side in the tire
width direction toward the outer circumferential main grooves and then end.
[0012]
A portion of an edge portion in contact with the circumferential main
grooves in the inside land portion and the intermediate land portions is
preferably provided with a chamfer.
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[0013]
A width of a land portion in a region on the inner side of the
circumferential shallow grooves in the tire width direction is preferably
greater
than a width of a land portion in a region on the outer side of the
circumferential shallow grooves in the tire width direction in the
intermediate
land portions.
EFFECT OF THE INVENTION
[0014]
The tire of the present invention demonstrates an excellent balance of
abrasion resistance on dry road surfaces, wet turning performance, and
steering
stability on snow. That is, abrasion resistance on dry road surfaces is
maintained while demonstrating excellent wet turning performance and steering
stability on snow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015]
FIG. 1 is a visual appearance view of an entire tire of an embodiment of
the present invention.
FIG. 2 is a meridian cross-sectional view of a portion of the tire
illustrated in FIG. 1.
FIG. 3 is a view as seen in plan development view to allow for easy
understanding of a tread pattern of the tire of the embodiment.
FIG. 4 is an enlarged view focusing on an inside land portion and
intermediate land portions in the tread pattern illustrated in FIG. 3.
FIG. 5A is a cross-sectional view along the line Va¨Va illustrated in FIG.
3 of the tread surface of the tire of the embodiment.
FIG. 5B is a cross-sectional view along the line Vb¨Vb illustrated in FIG.
3 of the tread surface of the tire of the embodiment.
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FIG. 6A is a view of an enlargement of a region A illustrated in FIG. 4.
FIG. 6B is a view of an enlargement of a region B illustrated in FIG. 4.
FIG. 6C is a view of an enlargement of a region C illustrated in FIG. 4.
BEST MODE FOR CARRYING OUT THE INVENTION
[0016]
The following is a detailed description of the pneumatic tire according to
the present invention.
FIG. 1 illustrates a visual appearance of a pneumatic tire 1 of an
embodiment of the present invention.
The pneumatic tire (hereafter referred to as a tire) 1 is a tire for a
passenger car.
The structure and rubber members of the tire 1 of the present invention
may be either publicly known or novel, and are not particularly limited in the
present invention.
[0017]
As illustrated in FIG. 2, the tire 1 includes a tread portion 2, a side wall
3,
a bead 4, a carcass layer 5, and a belt layer 6. FIG. 2 is a meridian
cross-sectional view illustrating a portion of the tire 1. In addition, the
tire 1
includes an inner liner layer, and the like, that are not illustrated in the
drawings.
The side wall 3 and the bead 4 are each formed as pairs that are arranged on
both sides in the tire width direction so as to sandwich the tread portion 2.
The tread portion 2, the bead 4, the belt layer 6, the inner liner, and the
like may be either publicly known or novel, and are not particularly limited
in
the present invention.
[0018]
The tire 1 of the present invention has a tread pattern 10 formed in the
tread portion as illustrated in FIG. 3. FIG. 3 is a view as seen in plan
development view to allow for easy understanding of the tread pattern 10 of
the
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tire 1 of the present invention. The tire 1 having the tread pattern 10 may be
suitably used as a tire for a passenger car. The dimensions of circumferential
main grooves, lug grooves, sipes, ground contact widths, chamfers,
circumferential shallow grooves, shoulder lug grooves, and land portion blocks
which are explained below are numerical examples for a tire for a passenger
car.
[0019]
The tire 1 of the present invention has information of a tire mounting
orientation, which side of the tire faces outward from the vehicle,
predetermined. The reference numeral CL in FIG. 3 refers to a tire equatorial
line. While the tire 1 is mounted so that the region of the tread pattern 10
on
the left side of the tire equatorial line CL in FIG. 3 is located inward to a
vehicle, and the region of the tread pattern 10 on the right side of the tire
equatorial line CL in FIG. 3 is located outward from the vehicle, the tire may
be
mounted so that the regions are located inward to and outward from the vehicle
in the reverse manner.
[0020]
While the tire 1 is mounted on a vehicle, the tread pattern 10 comes into
contact with the road surface in a region in the tire width direction
indicated by
a ground contact width 11w. Note that the hatched regions in the tread pattern
are regions further outside in the tire width direction than ground contact
edges.
The ground contact edges are determined as described below. The
ground contact edges are end portions in the tire width direction of a ground
contact patch when the tire 1 is brought into contact with a horizontal
surface
under conditions in which the tire 10 is fitted to a regular rim and inflated
to a
regular inner pressure of 180 kPa, and a load to be applied is set to 88% of a
regular load. Herein, "regular rim" includes a "standard rim" defined by the
Japan Automobile Tyre Manufacturers Association Inc. (JATMA), a "design
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rim" defined by the Tire and Rim Association, Inc. (TRA), and a "measuring
rim" defined by the European Tyre and Rim Technical Organisation (ETRTO).
While "regular inner pressure" includes "maximum air pressure" defined by
JATMA, the maximum value in "tire load limits at various cold inflation
pressures" defined by TRA, and "inflation pressures" defined by ETRTO, the
regular inner pressure is set to 180 kPa when the tire is for a passenger car.
Note that "regular load" includes "maximum load resistance" defined by
JATMA, the maximum value in "tire load limits at various cold inflation
pressures" defined by TRA, and "load capacity" defined by ETRTO.
[0021]
The tire width direction in the present invention refers to an extension
direction of the rotational center axis of the tire 1, and the tire
circumferential
direction refers to a rotation direction of the rotation surface of the tread
surface,
the rotation surface being formed when the tire 1 rotates around the tire
rotational center axis. The above directions are expressed in FIG. 3. The tire
rotation direction of the tread pattern 10 of the present invention is not
particularly limited.
The tire 1 of the present invention may have a pitch with the same
dimensions as the tread pattern 10 arranged in the tire circumferential
direction,
or the tire 1 may have a plurality of types of pitches with different
dimensions
from the tread pattern 10 arranged in the tire circumferential direction to
allow
for a pitch variation.
[0022]
The tread pattern 10 is provided with a circumferential main groove
group including four circumferential main grooves 11, 13, 15, 17 parallel to
the
tire circumferential direction, lug grooves 31, 33, 35, and circumferential
shallow grooves 41, 43.
[0023]
(Circumferential main groove group)
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The circumferential main groove group includes two outer
circumferential main grooves 11, 13 and two inner circumferential main
grooves 15, 17. The outer circumferential main grooves 11, 13 are disposed
on the outer side in the tire width direction of the inner circumferential
main
grooves 15, 17. The two inner circumferential main grooves 15, 17 are
disposed so as to be interposed between the outer circumferential main grooves
11, 13. The tire center line CL runs between the inner circumferential main
groove 15 and the inner circumferential main groove 17 in the tire width
direction. The groove depths of the outer circumferential main grooves 11, 13
and the inner circumferential main grooves 15, 17 are the same each other, but
may be different in another embodiment. The total amount of the groove
widths of the outer circumferential main grooves 11, 13 and the inner
circumferential main grooves 15, 17 is preferably from 15 to 25% of the ground
contact width llw from the point of view of wet performance.
[0024]
(Lug grooves)
The lug grooves 31, 33, 35 are grooves that cross the region of an inside
land portion 21 and the region of intermediate land portions 23, 25. Each of
the lug grooves 31, 33, 35 has a plurality of grooves spaced with intervals in
the
tire circumferential direction. The lug grooves 31, 33, 35 may each extend in
a substantially straight line or may extend in a moderately curved manner.
Groove widths 31w, 33w, 35w of the respective lug grooves 31, 33, 35 are all
the same in the tire width direction and are, for example, from 2 to 7 mm.
[0025]
Now, the inside land portion 21 and the intermediate land portions 23, 25
are explained.
The inside land portion 21 is a portion formed by being partitioned by
the two inner circumferential main grooves 15, 17. The tire center line CL
passes through the region of the inside land portion 21. A plurality of land
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portion blocks 22 is formed by the lug grooves 31 in the tire circumferential
direction in the region of the inside land portion 21. The lug grooves 31
extend in an inclined manner at an inclination angle Oce with respect to an X2
direction of the tire circumferential direction as illustrated in FIG. 4. FIG.
4 is
an enlarged view of a portion of the tread pattern 10. The inclination angle
Oce is, for example, from 60 to 85 . Due to the inclination angle being
closer
to the tire width direction than the tire circumferential direction in this
way, a
high block rigidity of the land portion blocks 22 can be achieved, and wet
turning performance and steering stability on snow can be improved with a
small steering angle while the vehicle is traveling. Note that when the lug
grooves 31 extend in a moderately curved manner, the inclination angle Oce
represents an inclination with respect to the direction of a straight line
connecting two center points at center positions in the width direction of the
lug
groove 31 in respective portions connecting the inner circumferential main
groove 15 and the outer circumferential main groove 17.
[0026]
The intermediate land portion 23 is a portion formed by being partitioned
by the outer circumferential main groove 11 and the inner circumferential main
groove 15. A plurality of land portion blocks 24 is formed in the tire
circumferential direction in the region of the intermediate land portion 23 by
the lug grooves 33. Furthermore, the intermediate land portion 25 is a portion
formed between the outer circumferential main groove 13 and the inner
circumferential main groove 17 by being partitioned by the outer
circumferential main groove 13 and the inner circumferential main groove 17.
A plurality of land portion blocks 26 is formed in the tire circumferential
direction in the region of the intermediate land portion 25 by the lug grooves
35.
[0027]
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When the lug grooves 33 and the lug grooves 35 advance from the outer
side in the tire width direction to the inner side, an orientation of a groove
inclination with respect to an X2 direction (a first direction of the tire
circumferential direction) of the lug grooves 33 is the same as an orientation
of
a groove inclination with respect to an X1 direction (a second direction that
is
the opposite direction of the first direction of the tire circumferential
direction)
of the lug grooves 35. In other words, the lug grooves 33 and the lug grooves
35 are inclined in the same orientation with respect to the X1 direction and
the
X2 direction of the tire circumferential direction, respectively. Note that
the
orientation of a groove inclination expresses a distinction between whether
the
groove inclination is in a range of 900 to 0 or in a range of 00 to 90
within a
range of -90 (900 in the counterclockwise direction) to 90 (90 in the
clockwise direction) with respect to the X1 direction or the X2 direction of
the
tire circumferential direction, and grooves inclined in the same range exhibit
the same orientation of the groove inclination, and grooves inclined in
different
angle ranges exhibit different orientations of the groove inclination.
Conversely, the above mentioned lug grooves 31 extend in inclining
orientation which is different from inclining orientation of the lug grooves
33,
35 inclination with respect to the tire circumferential direction.
Maneuverability
when turning left or right is assured by the above inclining orientations of
the
grooves.
[0028]
When the lug grove 33 advances from the outer side in the tire width
direction to the inner side in the tire width direction, the lug grooves 33
are bent
so that the groove inclination approaches the tire circumferential direction
at a
position P (see FIG. 4) where the lug grooves 33 intersect the circumferential
shallow groove 41. Specifically, as illustrated in FIG. 4, the lug grooves 33
are inclined at an inclination angle Oml with respect to the X2 direction on
the
outer side in the tire width direction of the position P and are inclined at
an
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inclination angle 0m2 with respect to the X1 direction on the inner side in
the
tire width direction of the position P. The inclination angle 0m2 is less than
the inclination angle Oml. As a result, while the lug grooves 33 advance from
the outer side in the tire width direction to the inner side in the tire width
direction, the lug grooves 33 are bent so that the groove inclination
approaches
the tire circumferential direction. The inclination angle Oml of the groove
inclination is, for example, from 60 to 85 . The inclination angle 0m2 is,
for
example, from 30 to 50 . Due to the lug grooves 33 having two types of
inclination angles in this way, when turning with a low steering angle to an
intermediate steering angle while the vehicle is traveling on dry road
surfaces,
wet road surfaces, and snow-covered road surfaces, excellent turning and
stability can be achieved. Note that the inclination angle Oml refers to an
inclination with respect to the tire circumferential direction of a straight
line
connecting two center points at center positions in the groove width direction
of
the lug grooves 33 in respective portions where the lug grooves 33 connect to
the outer circumferential main groove 11 and the circumferential shallow
groove 41 when the inner portion with respect to the circumferential shallow
groove 41 of the lug grooves 33 extends in a moderately curved manner.
Furthermore, the inclination angle 0m2 when the lug grooves 33 extend in a
moderately curved manner refers to an inclination with respect to the tire
circumferential direction of a straight line connecting two center points at
center positions in the groove width direction of the lug grooves 33 in
respective portions where the lug grooves 33 connect to the inner
circumferential main groove 15 and the circumferential shallow groove 41.
[0029]
When the lug grove 35 advances from the outer side in the tire width
direction to the inner side in the tire width direction, the lug grooves 35
are bent
so that the groove inclination approaches the tire circumferential direction
at
a position Q (see FIG. 4) where the lug grooves 35 intersect the
circumferential
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shallow groove 43. Specifically, as illustrated in FIG. 4, the lug grooves 35
are inclined at the inclination angle Om 1 with respect to the X1 direction on
the
outer side in the tire width direction of the position Q and are inclined at
the
inclination angle 0m2 with respect to the X2 direction on the inner side in
the
tire width direction inner side of the position Q. Note that when the inner
portions with respect to the circumferential shallow groove 43 of the lug
grooves 35 extend in a moderately curved manner, the inclination angle 0m1
refers to an inclination with respect to the tire circumferential direction of
a
straight line connecting two center points at center positions in the groove
width direction of the lug grooves 35 in respective portions where the lug
grooves 35 connect to the outer circumferential main groove 13 and the
circumferential shallow groove 43. Furthermore, when the lug grooves 35
extend in a moderately curved manner, the inclination angle 0m2 refers to an
inclination with respect to the tire circumferential direction of a straight
line
connecting two center points at center positions in the groove width direction
of
the lug grooves 35 in respective portions where the lug grooves 35 connect to
the inner circumferential main groove 17 and the circumferential shallow
groove 43. In another embodiment of the lug grooves 35, the inclination angle
on the outer side in the tire width direction of the position Q may be larger
than
the inclination angle on the inner side in the tire width direction of the
position
Q, or the inclination angle on the inner side in the tire width direction of
the
position Q may be smaller than the inclination angle on the outer side in the
tire
width direction of the position Q.
[0030]
The region of the intermediate land portion 23 on the inner side in the
tire width direction of the circumferential shallow groove 41 is preferably
wider
in the tire width direction than the region on the outer side in the tire
width
direction of the circumferential shallow groove 41 from the point of view of
assuring high block rigidity. The region of the intermediate land portion 25
on
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the inner side in the tire width direction of the circumferential shallow
groove
43 is preferably wider in the tire width direction than the region in the
outer
side in the tire width direction of the circumferential shallow groove 43 from
the same point of view.
[0031]
(Circumferential shallow grooves)
The circumferential shallow grooves 41, 43 are respectively provided in
the intermediate land portions 23, 25 and extend in the tire circumferential
direction.
The circumferential shallow grooves 41, 43 have raised bottoms and thus
have a shallower groove depth than the circumferential main grooves 11, 13,
15,
17. As a result, block rigidity and abrasion resistance on dry road surfaces
of
the intermediate land portions 23, 25 can be obtained while improving wet
turning performance. The groove depth of the circumferential shallow
grooves 41, 43 is preferably within 70%, more preferably from 30% to 50% of
the groove depth of the circumferential main grooves 11, 13, 15, 17 from the
point of view of assuring abrasion resistance.
Furthermore, the groove width of the circumferential shallow grooves 41,
43 is preferably from 5 to 15% of the length (width) in the tire width
direction
of the intermediate land portions 23, 25. Note that the length in the tire
width
direction of the intermediate land portions 23, 25 refers to the maximum
length
in the tire width direction of the land portion blocks 24, 26 on the tread
surface.
Furthermore, the circumferential shallow grooves 41, 43 are preferably
provided in positions in the tire width direction which are located 40% or
more
to less than 50% of the overall length (width) in the tire width direction of
each
of the intermediate land portions 23, 25 from the edges on the outer side in
the
tire width direction of the intermediate land portions 23, 25 to the edges on
the
inner side in the tire width direction due to abrasion resistance. That is,
the
width of land portions in the regions of the intermediate land portions 23, 25
on
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the inner side in the tire width direction of the circumferential shallow
grooves
41, 43 is preferably greater than the width of land portions in the regions of
the
intermediate land portions 23, 25 on the outer side in the tire width
direction of
the circumferential shallow grooves 41, 43.
Note that the circumferential shallow grooves are preferably not
provided in the region of the inside land portion 21 and in the regions of the
below-mentioned shoulder land portions 51, 53. The reason is the following.
The land portions 21, 51, 53 contribute greatly to wet turning performance and
steering stability on snow when braking and driving, but both wet turning
performance and abrasion resistance on dry road surfaces cannot be achieved if
the circumferential shallow grooves are provided in the land portions 21, 51,
53.
[0032]
(Sipes)
The tread pattern 10 further includes sipes 34, 36.
In the present invention, the sipes have a width of less than 1.5 mm and
have a groove depth of less than 5 mm. Furthermore, the lug grooves have a
groove width of 1.5 mm or more and have a groove depth of 5 mm or more.
The sipes 34, 36 are grooves that extend so as to be parallel to the lug
grooves 33, 35 in the respective intermediate land portions 23, 25. The sipes
34, 36 are each provided as two sipes in one land portion block 24, 26. Note
that, in another embodiment, the number of the sipes 34, 36 in one land
portion
block 24, 26 may be one or may be three or more.
[0033]
The sipes 34, 36 are respectively blocked within the intermediate land
portions 23, 25 without connecting with the inner circumferential main grooves
15, 17. As a result, abrasion resistance on dry road surfaces can be improved.
The sipes 34, 36 extend in a zigzag manner while deflecting in a direction
orthogonal to the extension direction of the sipes 34, 36 in the regions on
the
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inner side in the tire width direction of the circumferential shallow grooves
41,
43 and, as illustrated in FIG. 5A, extend toward the bottom portion in a
zigzag
manner while deflecting in a direction (left-right direction in drawing in
FIGS.
5A to 5C) orthogonal to the sipe depth direction (direction from bottom to top
in drawing in FIGS. 5A to 5C) from the tread surface toward the bottom
portion.
This shape of the sipes 34, 36 in the regions on the inner side in the tire
width
direction is also referred to hereinbelow as a three-dimensional shape. FIG.
5A is a view of line Va-Va in FIG. 3 and illustrates the state in which the
tread
portion 2 is in contact with a horizontal plane. Note that the reference
numerals represented in parentheses in FIGS. 5A to 5C are for indicating
elements in the region of the intermediate land portion 25 for ease of
description.
The respective regions on the inner side in the tire width direction of the
circumferential shallow grooves 41, 43 in the land portion blocks 24, 26 have
an inclination angle with respect to the tire circumferential direction of the
lug
grooves 33, 35 less than in the regions on the outer side in the tire width
direction of the circumferential shallow grooves 41, 43 whereby block rigidity
is reduced. As a result, block rigidity when braking and driving is configured
to be strengthened due to the above-mentioned three-dimensional shape of the
regions of the sipes 34, 36 on the outer side in the tire width direction of
the
circumferential shallow groove 41, 43.
[0034]
The sipes 34, 36 are respectively connected with the outer
circumferential main grooves 11, 13. The sipes 34, 36 preferably extend in a
linear manner respectively in the regions on the outer side in the tire width
direction of the circumferential shallow grooves 41, 43 and, as illustrated in
FIG.
5B extend in a planar manner in the sipe depth direction from the tread
surface
to the bottom portion. This shape of the sipes 34, 36 in the regions of the
outer side in the tire width direction is also referred to hereinbelow as a
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two-dimensional shape. FIG. 5B is a view of line Vb-Vb in FIG. 3 and
illustrates the state in which the tread portion 2 is in contact with a
horizontal
plane. Furthermore, a shape in which the sipes 34, 36 extend in a linear
manner does not include a shape in which the sipes 34, 36 extend in a zigzag
manner, but includes a shape in which the sipes 34, 36 extend along a straight
line and, for example, a shape in which the sipes 34, 36 extend in a
moderately
curved manner. Consequently, an extension of the sipes 34, 36 in a planar
manner includes an extension along a flat plane and, for example, an extension
along a moderately curved plane.
[0035]
The tread pattern 10 further includes sipes 32.
The sipes 32 are grooves that extend so as to be parallel to the lug
grooves 31 in the region of the inside land portion 21. The sipes 32 are
provided as two sipes in one land portion block 22. Note that, in another
embodiment, the number of the sipes 32 in one land portion block 22 may be
one or may be three or more. The sipes 32 have a three-dimensional shape,
thereby strengthening the block rigidity of the inside land portion 21 during
braking and driving. The sipes 32 connect with the inner circumferential main
grooves 15, 17. Note that, in another embodiment, the sipes 32 may have the
two-dimensional shape and may be blocked within the inside land portion 21
without connecting with the inner circumferential main grooves 15, 17.
[0036]
(Shoulder land portions)
The tread pattern 10 further has a shoulder land portion 51 on the outer
side in the tire width direction of the outer circumferential main groove 11.
Furthermore, the tread pattern 10 further has a shoulder land portion 53 on
the
outer side in the tire width direction of the outer circumferential main
groove
13.
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19
The regions of the shoulder land portions 51, 53 are respectively
provided with shoulder lug grooves 61, 63 extending from the outer side in the
tire width direction toward the outer circumferential main grooves 11, 13. The
shoulder lug grooves 61, 63 are respectively blocked part way through without
connecting with the outer circumferential main grooves 11, 13. As a result,
the shoulder land portions 51, 53 form continuous land portions that
continuously extend in the tire circumferential direction. Since the shoulder
land portions 51, 53 contribute greatly to braking performance and turning
performance, the formation of such continuous land portions allows a reduction
in block rigidity of the shoulder land portions 51, 53 to be suppressed and
allows abrasion resistance on dry road surfaces to be improved. Note that the
shoulder land portions 51, 53 preferably form the continuous land portions on
the sides in contact with the outer circumferential main grooves 11, 13 from
the
point of view of assuring good wet turning performance and steering stability
on snow.
Note that the distance between the shoulder lug groove 61 and the outer
circumferential main groove 11 in the region of the shoulder land portion 51,
that is, the width of a portion in which two adjacent blocks are joined in the
tire
circumferential direction to form the continuous land portions (joined width)
is
preferably from 5% to 20% of the length in the tire width direction between
the
outer circumferential main groove 11 and the ground contact edge. The length
is, for example, 15% in the present embodiment. Similarly, the distance
between the shoulder lug groove 63 and the outer circumferential main groove
13 in the region of the shoulder land portion 53 (joined width) is preferably
from 5% to 20% of the length in the tire width direction between the outer
circumferential main groove 13 and the ground contact edge. The length is,
for example, 15% in the present embodiment.
[0037]
CA 02877642 2014-12-22
The tips of the shoulder lug grooves 61, 63 on the inner side in the tire
width direction are formed in a tapered shape. Maximum groove widths 61w,
62w of the respective shoulder lug grooves 61, 63 are greater than the groove
widths (maximum groove widths) 31w, 33w, 35w of the respective lug grooves
31, 33, 35, and are, for example, from 4 to 8 mm. Thus, wet turning
performance and steering stability on snow are improved due to the greater
groove width of the shoulder land portions 51, 53 that contribute greatly
while
braking and driving. Note that the maximum groove width 61w of the
shoulder lug grooves 61 and the maximum groove width 62w of the shoulder
lug grooves 63 may be the same or different.
The shoulder lug grooves 61 extend in an inclined manner at Osh (see
FIG. 4) with respect to the X1 direction of the tire circumferential
direction, for
example, at from 75 to 90 . The shoulder lug grooves 63 extend in an
inclined manner at Osh (see FIG. 4) with respect to the X2 direction of the
tire
circumferential direction, for example, at from 75 to 90 . Due to the
shoulder lug grooves 61, 63 having inclination angles closer to the tire width
direction with respect to the tire circumferential direction in this way, a
high
block rigidity of the shoulder land portions 51, 53 is assured and wet turning
performance and steering stability on snow with a low steering angle is
improved. As illustrated in FIG. 4, the inclination angle Osh of the shoulder
lug grooves 61, 63 represents an inclination with respect to the tire
circumferential direction of a straight line connecting a point at the center
position of the width of the shoulder lug grooves 61, 63 in the tire
circumferential direction at the ground contact edge and a point at the center
position in the tire circumferential direction at an end portion on a side
with the
outer circumferential main grooves 11, 13. Note that the inclination angles of
the shoulder lug grooves 61, 63 may be the same or different.
[0038]
CA 02877642 2014-12-22
21
Furthermore, sipes 62, 64 are respectively provided in the regions of the
shoulder land portions 51, 53. Two sipes 62, 64 are provided between two
adjacent shoulder lug grooves 61, 63 in the tire circumferential direction.
The
number of the sipes 62, 64 provided in the shoulder land portions 51, 53
between the two adjacent shoulder lug grooves 61, 63 may be one or may be
three or more in another embodiment. Furthermore, the sipes 62, 64
preferably have the three-dimensional shape on the inner side in the tire
width
direction of the ground contact edge and preferably have the two-dimensional
shape on the outer side in the tire width direction of the ground contact
edge.
The rigidity of the shoulder land portions 51, 53 during braking and driving
can
be improved due to the sipes 62, 64 having the three-dimensional shape on the
inner side in the tire width direction of the ground contact edge.
Alternatively, the sipes 62, 64 include a two-dimensional shape portion
(first portion) that extends in a linear manner in the extension direction of
the
shoulder sipes 62, 64 and extends in planar manner in the sipe depth direction
from the tread surface of the sipes 62, 64 to the bottom portion of the sipes
62,
64, and a three-dimensional shape portion (second portion) that extends in a
zigzag manner while deflecting in a direction orthogonal to the extension
direction of the sipes 62, 64 and extends toward the bottom portion in a
zigzag
manner while deflecting in a direction orthogonal to the sipe depth direction
from the tread surface of the sipes 62, 64 toward the bottom portion of the
sipes
62, 64, and the sipes 62, 64 change from the two-dimensional shape portion to
the three-dimensional shape portion while advancing from the outer side in the
tire width direction toward the outer circumferential main grooves 11, 13 and
then end. The rigidity of the shoulder land portions 51, 53 during braking and
driving can be improved due to the sipes 62, 64 having the three-dimensional
shape on the sides close to the outer circumferential main grooves 11, 13.
[0039]
(Chamfers)
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22
The tread pattern 10 further has chamfers 21a, 23a, 25a, 51a, 53a.
As illustrated in FIG. 4, chamfers 21a are provided on some of the edge
portions of the inside land portion 21 in contact with the inner
circumferential
main grooves 15, 17. As a result, an edge amount of the inside land portion 21
is increased, and wet turning performance and steering stability on snow are
improved. Conversely, since the chamfers 21a are provided on some of the
edge portions, the block rigidity is not excessively reduced, and abrasion
resistance on dry road surfaces is assured.
The chamfers 21a are provided on both sides in the tire width direction
of each of the land portion blocks 22 as illustrated in FIG. 6B, and the
chamfers
21a are each machined so that a chamfer depth thereof is greater toward both
sides in the tire circumferential direction. FIG. 6B is an enlarged view of a
region encircled by B in FIG. 4 for explaining the chamfer 21a. The depth of
the chamfer 21a is preferably 50% or less, more preferably from 10% to 30% of
the groove depth of the inner circumferential main grooves 15, 17 from the
point of view of abrasion resistance.
[0040]
As illustrated in FIG. 4, chamfers 23a are provided on some of the edge
portions of the intermediate land portion 23 in contact with the outer
circumferential main groove 11. Furthermore, chamfers 25a are provided on
some of the edge portions of the intermediate land portion 25 in contact with
the outer circumferential main groove 13. In such a configuration, edge
amounts of the intermediate land portions 23, 25 are increased, and wet
turning
performance and steering stability on snow are improved. Furthermore, since
the chamfers 23a, 25a are provided on some of the edge portions, the block
rigidity is not excessively reduced and abrasion resistance on dry road
surfaces
is assured. FIG. 6C is an enlarged view of a region encircled by C in FIG. 4
for explaining the chamfer 25a. Note that the reference numerals represented
in parentheses in FIG. 6C are for indicating the elements in the region of the
CA 02877642 2014-12-22
23
intermediate land portion 23 for ease of description. The chamfers 23a may be
provided on the edge portions of the intermediate land portion 23 in contact
with the inner circumferential main groove 15. Furthermore, the chamfers 25a
may be provided on the edge portions of the intermediate land portion 25 in
contact with the inner circumferential main groove 17. The depth of the
chamfers 23a, 25a is preferably 50% or less, and more preferably from 10% to
30% of the groove depth of the circumferential main grooves 11, 13, 15, 17
from the point of view of abrasion resistance.
[0041]
As illustrated in FIG. 4, chamfers 51a, 53a are respectively provided on
some of the edge portions in contact with the outer circumferential main
grooves 11, 13 of the shoulder land portions 51, 53. As a result, edge amounts
of the shoulder land portions 51, 53 are increased, and wet turning
performance
and steering stability on snow are improved. The reason why the chamfers
51a, 53a are provided is to assure abrasion resistance on dry road surfaces
without excessively reducing the rigidity of the shoulder land portions 51, 53
as
some of edges. The chamfers 51a, 53a each have two surfaces adjacent to
each other in the tire circumferential direction and having different
inclinations
as illustrated in FIG. 4 and FIG. 6A. FIG. 6A is an enlarged view of a region
encircled by A in FIG. 4 for explaining the chamfer 51a. Note that the
reference numerals represented in parentheses in FIG. 6A are for indicating
the
elements in the region of the shoulder land portion 53 for ease of
description.
The depth of the chamfers 51a, 53a is preferably 50% or less, and more
preferably from 10% to 30% of the groove depth of the circumferential main
grooves 11, 13.
[0042]
The groove depths of the circumferential main grooves 11, 13, 15, 17
may be the same as each other or different.
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24
The maximum depths of the chamfers 21a, 23a, 25a, 51a, 53a may be the
same as each other or different.
The groove depths of the circumferential shallow grooves 41, 43 may be
the same as each other or different.
The maximum widths of the land portion blocks 24, 26 may be the same
as each other or different.
The sipes 34, 36 may not be arranged parallel to the lug grooves 33, 35.
The sipes 34, 36 may be respectively connected with the outer circumferential
main grooves 11, 13. Furthermore, the sipes 34, 36 may be respectively
blocked within the intermediate land portions 23, 25 without connecting with
the inner circumferential main grooves 15, 17. The tread pattern 10 may not
have the sipes 34, 36.
The sipes 34, 36 may be provided only on one side of the circumferential
shallow grooves 41, 43.
The shoulder lug grooves 61, 63 may be respectively connected with the
outer circumferential main grooves 11, 13, thereby forming a plurality of land
portion blocks in the tire circumferential direction. The tread pattern 10 may
not have the shoulder lug grooves 61, 63.
The groove width of the shoulder lug grooves 61, 63 may be equal to or
less than the groove width of the lug grooves 31, 33, 35.
The number of circumferential main grooves is not limited to four and
may be five or more. In this case, three inner circumferential main grooves
can be provided.
[0043]
The tread pattern 10 in the above pneumatic tire 1 has the four
circumferential main grooves 11, 13, 15, 17 and the lug grooves 31 and the
sipes 32 in the region of the inside land portion 21, and further has the lug
grooves 33, 35 and the sipes 34, 36 in the regions of the intermediate land
CA 02877642 2014-12-22
portions 23, 25, whereby the basic wet turning performance and the steering
stability on snow required for tire performance are assured.
Furthermore, the lug grooves 33, 35 provided in the respective
intermediate land portions 23, 25 are inclined in the same orientation with
respect to directions (X1 direction and X2 direction) different from each
other
of the tire circumferential direction, and the lug grooves 33, 35 are inclined
in
an opposite orientation with respect to the tire circumferential direction of
the
lug grooves 31 provided in the region of the inside land portion 21, and
moreover, the lug grooves 33, 35 are bent so that the groove inclination
approaches the tire circumferential direction (X1 direction, X2 direction) at
the
points P, Q where the lug grooves 33, 35 respectively intersect the
circumferential shallow grooves 41, 43, whereby wet turning performance and
steering stability on snow are improved.
Furthermore, when the configuration of the shoulder lug grooves 61, 63
is added to the configuration of the lug grooves 31, 33, 35, the tread pattern
10
has grooves with various orientations and inclination angles, whereby wet
turning performance and steering stability on snow are further improved.
Furthermore, the regions of the intermediate land portions 23, 25 are
respectively provided with the circumferential shallow grooves 41, 43 having a
groove depth less than the groove depth of the circumferential main grooves
11,
13, 15, 17, whereby abrasion resistance is assured.
[0044]
The sipes 34, 36 are provided respectively in the regions of the
intermediate land portions 23, 25 and are blocked within the intermediate land
portions 23, 25 without connecting with the inner circumferential main grooves
15, 17, whereby abrasion resistance on dry road surfaces is assured.
The sipes 34, 36 have the three-dimensional shape in the regions on the
inner side in the tire width direction of the circumferential shallow grooves
41,
43, whereby block rigidity during braking and driving is improved.
CA 02877642 2014-12-22
26
[0045]
The formation of the continuous land portions extending continuously in
the tire circumferential direction in the regions of the shoulder land
portions 51,
53 allows a high block rigidity of the shoulder land portions 51, 53 to be
assured and allows abrasion resistance on dry road surfaces to be improved.
Furthermore, a reduction in block rigidity of the shoulder land portions 51,
53
is prevented and abrasion resistance on dry road surfaces is assured.
The maximum groove width of the shoulder lug grooves 61, 63 is greater
than the groove width of the lug grooves 31, 33, 35, whereby wet turning
performance and steering stability on snow are improved.
Chamfers are provided on some of the edge portions in the tire width
direction of the inside land portion 21 and the intermediate land portions 23,
25,
whereby the edge amounts are increased, and wet turning performance and
steering stability on snow are improved.
[0046]
(Other forms of tread pattern)
The sipes 34, 36 may not be provided in parallel with the lug grooves
33, 35. The sipes 34, 36 may be connected with the outer circumferential
main grooves 11, 13. Further, the sipes 34, 36 may be blocked within the
intermediate land portions without connecting with the inner circumferential
main grooves 15, 17. The tread pattern 10 may not include the sipes 34, 36.
The sipes 34, 36 may have a two-dimensional shape on the inner side of
the circumferential shallow grooves 41, 43 and a three-dimensional shape on
the outer side of the circumferential shallow grooves 41, 43. Alternatively,
on
both sides of the inner side and the outer side, the sipes 34, 36 may have a
two-dimensional shape or three-dimensional shape. The sipes 34, 36 may
have a combination of the two-dimensional shape and a three-dimensional
shape on at least one of the two sides. One of the sipes 34, 36 may be
CA 02877642 2014-12-22
27
provided on one side of the two sides against the provided two circumferential
shallow grooves 41, 43.
The shoulder lug grooves 61, 63 may be connected with the outer
circumferential main grooves 11, 13 to form a plurality of land portion blocks
arranged in the tire circumferential direction. The tread pattern 10 may not
include the shoulder lug grooves 61, 63. The groove width of the shoulder lug
grooves 61, 63 may be not greater than the groove width of the lug grooves 31,
33, 35.
The number of the circumferential groves provided on the tread surface
is not limited to four. The number may be five or more. In this case, the
tread pattern may include three or more of the inner circumferential main
grooves.
[0047]
(EXAMPLE)
Test tires were manufactured to study the effects of the tread pattern 10
of the tire 1 of the present invention.
The tire size was P265/70R17 113T. Tires with a rim size of 17x7.5J
were manufactured provided with the tread patterns according to the
specifications described in the following Tables 1 and 2. A front-engine,
front-drive (FF) vehicle with an engine displacement of 2 liters was used as a
test vehicle for studying tire performance. The inner pressure of all of the
front wheels and the rear wheels was set to 230 kPa.
Wet turning performance, steering stability on snow, and abrasion
resistance were evaluated for tire performance of the test tires as described
below.
[0048]
The test vehicle was driven for 5 laps at a limited speed on an R30
(radius 30 m) turning course of a wet road surface of an outdoor tire testing
facility having a film of water with a depth of 1 mm in, and the average
lateral
CA 02877642 2014-12-22
28
acceleration at this time was measured for evaluating the wet turning
performance. The evaluation was performed by expressing the inverse of the
measured values as an index and taking the inverse of the measured value of
the
tire of the Conventional Example 1 as 100. A larger index signifies a
correspondingly superior wet turning performance.
For the steering stability on snow, the measurement was made in the
same way as the measurement of the wet turning performance, except for the
road surface being changed from a wet road surface having a film of water with
a depth of 1 mm to a snow-covered road surface. The evaluation was
performed by expressing the inverse of the measured values as an index and
taking the inverse of the measured value of the tire of the Conventional
Example 1 as 100. A larger index signifies a correspondingly superior
steering stability on snow.
The abrasion resistance was evaluated by measuring the amount of
abrasion after the test vehicle was driven for 2000 km on public roads. The
evaluation was carried out by taking the inverse of the measurement values and
expressing the inverse of the measurement values of the tire of the
Conventional Example 1 as 100. A larger index signifies a correspondingly
superior abrasion resistance.
[0049]
The respective evaluation results are described in Tables 1 and 2.
Note that "not parallel" signifies that the direction in which the sipes
extend is in the opposite orientation with respect to the tire width direction
to
the direction in which the lug grooves extend inside the region of the same
intermediate land portion, and "parallel" signifies that the direction in
which the
sipes extend is in the same orientation with respect to the tire width
direction as
the direction in which the lug grooves extend inside the region of the same
intermediate land portion, in Tables 1 and 2. Furthermore, the groove depth of
the circumferential shallow grooves signifies a percentage (%) with respect to
CA 02877642 2014-12-22
29
the groove depth of the circumferential main grooves. Whether the shoulder
lug grooves are blocked or not indicates that the shoulder lug grooves 61, 63
are
blocked part way through without connecting with the outer circumferential
main grooves 11, 13, or indicates that the shoulder lug grooves 61, 63 are
connected with the outer circumferential main grooves 11, 13. The sipes in
the intermediate land portions all had the two-dimensional shape in the
Working
Example 3.
[0050]
[Table 1]
Working Working
Conventional Working Working Working
Example Example
Example 1 Example 1 Example 2 Example 3
4 5
Presence or
absence of
lug grooves
in inside
land portion, Present,
Present,
Present, Present, Present,
inclination 70 70
Absent 70 degrees 70 degrees 70 degrees
angle of lug degrees degrees
mm 5 mm 5 mm
grooves, 5 mm 5 mm
maximum
groove
width
thereof
'
Presence or
absence of
bends in lug
grooves in Bend Bend
intermediate Bend Bend Bend 70 70
No bend
land 70 degrees 70 degrees 70 degrees degrees degrees
70 degrees
portions, 45 degrees 45 degrees 45 degrees 45 45
5 mm
inclination 5 mm 5 mm 5 mm degrees degrees
angle of lug 5 mm 5 mm
grooves,
maximum
groove
CA 02877642 2014-12-22
width
thereof
Presence or
absence of
circumferent
ial shallow Present, Present, Present, Present,
Present,
grooves, Absent 30% 30% 30% 30% 30%
groove
depth
thereof
Sipes in
intermediate
Not
land portion Not parallel Parallel Parallel Parallel
Parallel
parallel
(parallel,
not parallel)
Presence or
absence of
sipes with
three-dimen
sional shape Absent Present Present Absent Present Present
in
intermediate
land
portions
Inclination
angle of
shoulder lug
85 85
grooves, 70 degrees 85 degrees 85 degrees 85 degrees
degrees degrees
maximum 5 mm 5 mm 5 mm 5 mm
5 mm 5 mm
groove
width
thereof
Presence or
absence of
blocking in Absent Present Present Present Absent Present
shoulder lug
grooves
Presence or
Absent Present Present Present Present Absent
absence of
CA 02877642 2014-12-22
31
chamfers in
land
portions
Steering
stability on 100 104 104 106 106 102
snow
Wet turning
100 104 104 106 106 102
performance
Abrasion
100 104 103 100 101 107
resistance
[0051]
[Table 2]
Comparative Comparative Comparative
Example 1 Example 2 Example 3
Presence or absence
of lug grooves in
inside land portion, Present, Present, Present,
inclination angle of 70 degrees 70 degrees 70 degrees
lug grooves, 5 mm 5 mm 5 mm
maximum groove
width thereof
Presence or absence
of bends in lug
grooves in Bend Bend
intermediate land 70 degrees 70 degrees No bend
portions, inclination 45 degrees 45 degrees 70 degrees
mm
angle of lug grooves, 5 mm 5 mm
maximum groove
width thereof
Presence or absence
of circumferential Present, Present,
shallow grooves, Absent 100% 60%
groove depth thereof
Sipes in intermediate
land portions
Parallel Parallel Parallel
(parallel, not
parallel)
CA 02877642 2014-12-22
32
Presence or absence
of sipes with
three-dimensional
Present Present Present
shape in
intermediate land
portions
Inclination angle of
shoulder lug 85 degrees 85 degrees 85 degrees
grooves, maximum 5 mm 5 mm 5 mm
groove width thereof
Presence or absence
of blocking in Present Present Present
shoulder lug grooves
Presence or absence
of chamfers in land Present Present Present
portions
Steering stability on
101 105 102
snow
Wet turning
101 105 102
performance
Abrasion resistance 100 95 95
[0052]
As can be seen in Table 1 and Table 2, when the lug grooves were bent in
the region of the intermediate land portions and the groove depth of the
circumferential shallow grooves was less than the groove depth of the
circumferential main grooves (Working Examples 1 to 5), the balance between
abrasion resistance on dry road surfaces, and wet turning performance and
steering stability on snow was more superior than when the above was not true
(Comparative Examples 1 to 3). That is, abrasion resistance on dry road
surfaces was maintained (index of 100 or more), and wet turning performance
and steering stability on snow were superior (index of 102 or more).
In particular, the tires of the Working Examples 1 to 5 in which the
groove depth of the circumferential shallow grooves was 30% of the groove
depth of the circumferential main grooves demonstrated a balance between
CA 02877642 2014-12-22
33
steering stability on snow, wet turning performance, and abrasion resistance
more superior than that of the tire of the Comparative Example 2 in which the
lug grooves were bent in the region of the intermediate land portions while
the
groove depth of the circumferential shallow grooves was the same (100%) as
the groove depth of the circumferential main grooves.
[0053]
The pneumatic tire of the present invention was described in detail above.
However, it should be understood that the present invention is not limited to
the
above embodiments, but may be improved or modified in various ways so long
as these improvements or modifications remain within the scope of the present
invention.
REFERENCE NUMBER
[0054]
1 Pneumatic Tire
2 Tread portion
Tread pattern
11, 13 Outer circumferential main grooves
15, 17 Inner circumferential main grooves
21 Inside land portion
21a, 23a, 25a, 51a, 53a, Chamfer
23, 25 Intermediate land portions
22, 24, 26 Land portion block
31, 33, 35 Lug grooves
31w, 33w, 35w Lug groove maximum groove width
34, 36 Sipes
41, 43 Circumferential shallow grooves
51, 53 Shoulder land portions
61, 63 Shoulder lug grooves
CA 02877642 2014-12-22
34
61w, 62w Shoulder lug groove maximum groove width
Oml, 0m2 Lug groove inclination
CL Center line
P, Q Lug groove and circumferential shallow groove intersecting position
X1 First direction in tire circumferential direction
X2 Second direction in tire circumferential direction
